1. Field of the Invention
The invention relates to a gas heating boiler with a burner and without a blower, with partial load control, comprising a combustion chamber a plurality of heat exchanger elements located above said combustion chamber a Venturi tube with a nozzle and an air damper in the wall of the combustion chamber, through which the partial air volumes required for the combustion process are suctioned into the combustion chamber.
2. Background of the Art
It is known that, with respect to the time interval constituting a heating period, heating boilers for the heating of dwelling space exhibit a mean load amounting only to approximately 25% of total time. As the result of this low rate of utilization high standby losses occur caused in particular by the convective air flow through the boiler during the long downtime periods, whereby the heat of the boiler is transferred by the waste gas exhaust to the atmosphere. While the throttling of the burner to extend operating periods without interfering with the utilization of combustion air leads to the desired reduction of downtime losses, it also results in a disproportional decline in the operating efficiency of the boiler, so that this method of solving the problem is not feasible.
It is known to operate gas fired heating boilers in a so-called "modulated burner mode" in order to eliminate this disadvantage, whereby--by means of gas jet pressure regulation--the volume of the combustion gas is controlled and therefore the air suctioned through the Venturi tube modified to some extent. All measurements in this area have demonstrated, however, that this mode of operation does not lead to an appreciable increase in boiler efficiency, as while if the pressure at the jet is reduced, the air suctioned in through the Venturi tube is also reduced to an approximately proportional extent. On the other side the so-called secondary air component suctioned in by the flame not only remains practically unchanged, but is even increased in part. The result is that if the pressure at the jet is reduced, the excess air is increased, which overall leads to a reduction of boiler efficiency in spite of the decreasing flue gas temperatures, which cannot be compensated for by the reduction in standby losses achieved. Altogether therefore this method does not lead to an improvement in the annual efficiency which is decisive in view of boiler efficiency.
To eliminate the aforedescribed disadvantages, it is further known to introduce the secondary air component through an air damper arranged in the housing under the burner and to control it by that the damper is opened and closed continuously in a proportional dependence on the gas pressure determined by the jet of the burner. A solution of this type is sensitive--in addition to the high cost--in view of the necessary accurate coupling of the gas supply and the position of the damper. It further has little flexibility as the gas pressure and thus the output must be regulated as a function of gas quality by the position of the air damper.
It is finally known to insert dampers into the path of the flue gases, which in case of a partial load stage partially close the flue gas conduit, whereby the flow resistance is increased and thus the supply of secondary air reduced. In this case a reduction of boiler efficiency in the half load stage is avoided, but the disadvantage of the solution, in addition to the low flexibility represented by the exact adjustment of the partial load stage as a function of the prevailing gas quality, consists of a reduction in safety, as throttles or closures in the flue gas conduit by means of moving inserts are considered a risk factor. Furthermore, dampers of this type must always be provided with a certain clearance to insure their frictionless movement at the prevailing temperature.